In recent years, there have been required an increase in reliability, a decrease in cost, and downsizing for a permanent-magnet type rotating electrical machine such as a permanent magnet motor. In order to meet those requirements, rotation-sensor-less drive technologies capable of dispensing with a rotation detection device for a motor such as an optical encoder or a resolver have been developed.
As one of rotation-sensor-less drive methods for the permanent-magnet type rotating electrical machine, there is proposed a high frequency superimposing method enabling estimation of magnetic pole positions of a motor even when the motor is not rotating (for example, refer to Patent Literature 1). The high frequency superimposing method involves applying a high frequency voltage independent of voltages for generating a torque to armature windings of the motor, and using a difference between a d-axis current and a q-axis current caused by a dependency of the inductance of the motor on a rotor position (saliency) to detect the position of the rotor.
Moreover, as the motor applied to the high frequency superimposing method, namely, as the motor for the rotation-sensor-less drive using the dependency of the inductance of the motor on the rotor position (saliency), an interior magnet motor having the saliency is used (for example, refer to Patent Literature 2). In the interior magnet motor, permanent magnets are embedded in a rotor iron core, and a stator iron core is integrally structured, and has an opening shape, thereby enabling detection of an initial magnetic pole position when a power supply is turned on.